When irradiated with infrared light, some molecules such as metal phthalocyanine vibrate and generate small localized magnetic fields. Researchers have calculated these effects and aim to test and experimentally manipulate these fields for possible applications in quantum computing. Credit: SciTechDaily.com
Physicists at TU Graz have determined that certain molecules can be stimulated by pulses of infrared light to generate small magnetic fields. If experimental evidence is also successful, this technique could potentially be applied to quantum computer circuits.
When molecules absorb infrared light, they begin to vibrate as they gain energy. Andreas Hauser from the Institute of Experimental Physics at the Graz University of Technology (TU Graz) used this well-understood process as a basis to explore whether these vibrations could be harnessed to produce magnetic fields. Since atomic nuclei carry a positive charge, the movement of these charged particles results in the creation of a magnetic field.
Using the example of metal phthalocyanines – planar ring-shaped dye molecules – Andreas Hauser and his team have now calculated that, due to their high symmetry, these molecules actually generate small magnetic fields in the nanometer range when pulsed infrared act on them.
According to calculations, it should be possible to measure quite low but very localized field strength using nuclear magnetic resonance spectroscopy. The researchers have published their results in Journal of the American Chemical Society.
Circular dance of molecules
For the calculations, the team drew on preliminary work from the early days of laser spectroscopy, some of which was several decades old. They also used state-of-the-art electron structure theory on supercomputers at the Vienna Science Group and TU Graz to calculate how phthalocyanine molecules behave when irradiated with circularly polarized infrared light. What happened was that circularly polarized, i.e. spirally twisted, light waves excite two molecular vibrations at the same time at right angles to each other.
Andreas Hauser from the Institute of Experimental Physics at TU Graz. Credit: Lunghammer – TU Graz
“As any rumba couple knows, the right combination of forward-backward and left-right creates a small, closed loop. And this circular movement of each affected atomic nucleus actually creates a magnetic field, but only a very local one, with dimensions in the range of a few nanometers,” says Andreas Hauser.
Molecules as circuits in quantum computers
By selectively manipulating the infrared light, it is even possible to control the strength and direction of the magnetic field, explains Andreas Hauser. This would turn the molecules into high-precision optical switches, which could perhaps also be used to build circuits for a quantum computer.
Schematic representation of a metal phthalocyanine molecule settling into two vibrations (red and blue), creating a spin electric dipole moment (green) in the molecular plane and thus a magnetic field. Credit: Wilhelmer/Diez/Krondorfer/Hauser – TU Graz
Experiments as the next step
Together with colleagues from the Institute of Solid State Physics at TU Graz and a team at the University of Graz, Andreas Hauser now wants to prove experimentally that molecular magnetic fields can be generated in a controlled manner.
“For tests, but also for future applications, the phthalocyanine molecule must be placed on a surface. However, this changes the physical conditions, which in turn affects the excitation caused by the light and the characteristics of the magnetic field”, explains Andreas Hauser. “So we want to find a support material that has minimal impact on the desired mechanism.”
In the next step, the physicist and his colleagues want to calculate the interactions between the deposited phthalocyanines, the support material and infrared light before testing the most promising variants in experiments.
Reference: “Molecular pseudorotation in phthalocyanines as a tool for nanoscale magnetic field control” by Raphael Wilhelmer, Matthias Diez, Johannes K. Krondorfer and Andreas W. Hauser, 14 May 2024, Journal of the American Chemical Society.
DOI: 10.1021/jacs.4c01915
The study was funded by the Austrian Science Fund.